Primitive Types

The table in Appendix D, Primitive Types, lists the eight primitive types in Java. Like its predecessor languages C and C++, Java requires all variables to have a type. For this reason, Java is referred to as a strongly typed language.

In C and C++, programmers frequently have to write separate versions of programs to support different computer platforms, because the primitive types are not guaranteed to be identical from computer to computer. For example, an int value on one machine might be represented by 16 bits (2 bytes) of memory, while an int value on another machine might be represented by 32 bits (4 bytes) of memory. In Java, int values are always 32 bits (4 bytes).

Portability Tip 4.1

Unlike C and C++, the primitive types in Java are portable across all computer platforms that support Java. Thanks to this and Java's many other portability features, a programmer can write a program once and be certain that it will execute on any computer platform that supports Java. This capability is sometimes referred to as WORA (Write Once, Run Anywhere).

Each type in Appendix D is listed with its size in bits (there are eight bits to a byte) and its range of values. Because the designers of Java want it to be maximally portable, they use internationally recognized standards for both character formats (Unicode; for more information, visit www.unicode.org) and floating-point numbers (IEEE 754; for more information, visit grouper.ieee.org/groups/754/).

Recall from Section 3.5 that variables of primitive types declared outside of a method as fields of a class are automatically assigned default values unless explicitly initialized. Instance variables of types char, byte, short, int, long, float and double are all given the value 0 by default. Instance variables of type boolean are given the value false by default. Similarly, reference type instance variables are initialized by default to the value null.